Could there be Hydrogen Breathing Aliens?

Kepler-186f, the First Earth-size Planet in the Habitable Zone (Artist's Concept)

Credit: NASA/Ames/SETI Institute/JPL-Caltech


At the time of writing over 4000 known exoplanets have been discovered. This is the first step to identifying potentially habitable worlds and so where the search for extra-terrestrial life begins.


If you are looking for life outside our solar system, it makes sense to try and identify worlds similar to our own. After all, we know that life can develop on Earth, so looking for Earth like planets gives us the best chance of finding life that is similar to us.

Detecting exoplanets


The K2 spacecraft and its predecessor Kepler have provided NASA with information about many of these potential homes for life. They tend to be many light years away and so it is unlikely that we will visit them any time soon, or that any alien life will make it here either.
“Right now we know, for the first time, that small planets are very common,”: 

But as Sara Seager, a professor at the Massachusetts Institute of Technology and an exoplanet research pioneer has said, “Right now we know, for the first time, that small planets are very common.” So Maybe, even though we can't go and say 'hello', we might find evidence of life.

Planets are detected in a number of ways, they can be seen traversing the star that they are orbiting, for example, and by measuring the length and the frequency of the orbit, estimations can be made about the size of the planet.

The transit method also allows scientists to discover the composition of the planet's atmosphere by analyzing the light that passes through it. This spectral analysis has led tot he discovery of amongst, other things, water vapor and methane.

But for life as we know it to exist elsewhere water is not the only prerequisite. The life that we know about on our own planet requires an atmosphere rich in oxygen.

What about hydrogen?

But a new paper in Nature Astronomy argues that we should broaden the search from planets that have atmospheres similar to our own and include those that have an atmosphere rich in hydrogen.

Hydrogen is the lightest of gases and so escapes easily from the atmosphere. So for a planet to be able to maintain a hydrogen atmosphere it would have to be much more massive than the Earth - between two and ten times as big. It could also be further away from its home star as the greenhouse effect of a hydrogen atmosphere would warm the planet.

Both of these factors increase the number of prospective planets.

On Earth it is know that micro-organisms can live in a hydrogen rich environment, so the concept of hydrogen breathing life is not beyond belief.

Taking these things into account may mean that the number  of candidate planets for life could double. so NASA has its work cut out.

Reference

Seager, S., Huang, J., Petkowski, J.J. et al. Laboratory studies on the viability of life in H2-dominated exoplanet atmospheres. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1069-4

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